One who indulges in alcohol/marijuana/drugs and the like only on occasion-- especially during social events. Tasters do not have as much experience as non-tasters with a given substance, since "tasting" is usually associated with gratifying oneself on a low-intensity level.

(During a toast at a formal fraternity event)
Nate: "Here's a special toast to all the tasters tonight! Let's live la vida loca!"